Tuesday, May 6, 2014

If using oil based paint pour solvent into a paint tray and stroke brushes or rollers back and forth until the solvent dripping from them is clear. Moreover the oil based paint can be cleaned from the tools by using
•White spirit
•Turpentine and substitutes

White spirit also known as Stoddard solvent or mineral spirits, is a paraffin-derived clear, transparent liquid which is a common organic solvent used in painting and decorating. It is a mixture of aliphatic and alicyclic C7 to C12 hydrocarbons with a maximum content of 25% of C7 to C12 aromatic hydrocarbons. It is a mixture of aliphatic and alicyclic C7 to C12 hydrocarbons with a maximum content of 25% of C7 to C12 aromatic hydrocarbons. White spirit is the most widely used solvent in the paint industry. In households, white spirit is commonly used to clean paint brushes after decorating. Its paint thinning properties enable brushes to be cleaned (by preventing the paint from hardening and ruining the bristles), enabling them to be reused.

Turpentine substitute, also known as Mineral turpentine is an inexpensive petroleum-based replacement for the vegetable-based turpentine. It is commonly used as a paint thinner for thinning oil-based paint and cleaning brushes, and as an organic solvent in other applications.
Mineral turpentine is a hydrotreated light distillate of petroleum, and consists of a complex mixture of highly refined hydrocarbon distillates mainly in the C9-C16 range. The material is a colourless transparent liquid at room temperature, and immiscible to water. The liquid is highly volatile and the vapours are flammable. It can be a very dangerous inhalant.
Mineral turpentine has a characteristic unpleasant odour. Chemical manufacturers have developed a low odour version of mineral turpentine which contains less of the highly volatile shorter hydrocarbons.
The water based paint can be cleaned from tools using cold water. Remove water based paints with soap and wearer, working the bristles or nap until the water runs clear.

When brushes and roller cover are clean, use a spinner tool to remove excess solvent or water. Make sure to wipe clean and dry. When the tools are dry return them to the original wrappers and hand securely separately.

Oil-based (also known as solvent-based) coatings, such as paints, stains, and varnishes are amongst the oldest organic coating materials; in China, they have been known for more than 2000 years. Oil paints consist natural drying oils (e.g. linseed oil, China wood or tung oil, and soybean oil) which undergo autoxiadative polymerization in the presence of catalytic dries and atmospheric oxygen. Further constituents may include hard resins that general react with the drying oils at elevated temperature (230-2800C) to form oleo resinous binders. On account of the air sensitivity of the oils, heating mainly takes place under an inert gas atmosphere.
Conventional dispersion equipments (e.g. ball, roller or sand mills) are suitable for producing oil paints.

Oil based coatings are relatively environmentally friendly as long as hazardous solvents and toxic pigments (e.g. red lead or zinc chromate) are not used. The oil used in such paints have a low viscosity. They are therefore particularly suitable for priming coas o manually derusted steel surfaces since they wet and penetrate the residual layers of rust well, resulting in thorough coverage.
Oil based coatings are easily applied by conventional methods (e.g brushing, roller coating, spraying and dipping)
Oil-based coatings contain resins, solvents, pigments and additives. These coatings are harmful
to the environment because they contain petroleum distillates and pigments which, when
evaporated, can increase volatile organic compound (VOC) levels in the air.

Oil-based coatings can have adverse effects on your health if not used properly. If used in poorly
ventilated areas, the vapors from these products can irritate eyes, skin, and lungs, causing
headaches and nausea. The vapors can also contribute to respiratory problems, muscle
weakness and liver and kidney damage.

Oil-based coatings can also harm the environment if not disposed of properly. Never pour paint
down a storm drain or sewer system. This can pollute groundwater, rivers and streams.

Water based paints are synthetic resins and pigments, plus coalescing agents, that are kept dispersed in water by surfactants. They dry by evaporation of the water, the coalescing agents cause the particles of resin to fuse together as the water evaporates to form a continuous coating. It has a binder that is dissolved in water. In general, water-based paints are less toxic and contain fewer volatile organic compounds (VOCs) than solvent-based (also called oil-based or alkyd) paints. It is also known latex paint.

water based paints are based on acrylic, urethane, polyvinyl acetate (PVA) or epoxy dispersions. Acrylic emulsions are used in exterior applications where their non-yellowing characteristics as well as excellent weatherbility are outstanding. Water based urethanes are suited to uses where good flexibility and toughness are important , such as leather and polymer coatings, but their major drawback is their high cost. PVA and epoxies give good weathering resistance. Water based paints take longer to dry than many organic solvent based paints, and give a surface finish that is less good.

Water based paints must be protected from freezing and applied at a minimum temperature of 10 c. humidity and temperature control are critical for the drying time. A heat cure is sometime necessary. Pigments must be compatible with water. Metallic particles are usually coated before being mixed into the paint to prevent chemical reaction with water. Many conventional binders (alkyls, acrylics and expodies) can be made water soluble by chemically attaching polar groups such as carboxyl, hydroxyl and amide. Dispersions are very small particles of binders, less than 0.1 microns diameter, dispersed in water. Emulsions or latex differ from dispersions by having much larger particle sixe on the order of 0.1 micron or more. They are made by precipitation in water and therefore do not need to be dispersed mechanically.

Saturday, May 3, 2014

Proper surface preparation is essential for the success of any protective coating scheme. The importance of removing oil, grease, old coatings and surface contaminants (such as mill scale and rust on steel, laitance on concrete and zinc salts on galvanised surfaces) cannot be over emphasised.

The performance of any paint coating is directly dependent upon the correct and thorough preparation of the surface prior to coating. The most expensive and technologically advanced coating system will fail if the surface preparation is incorrect or incomplete.

Loosely adhering mill scale, rust and old paint coatings may be removed from steel by hand wire brushing, sanding, scraping and chipping. However, these methods are incomplete, and always leave a layer of tightly adhering rust on the steel surface.

A scraper is a single-edged tool used to scrape metal from a surface. This may be required where a surface needs to be trued, corrected for fit to a mating part, needs to retain oil (usually on a freshly ground surface), or even to give a decorative finish.

The task of scraping has been the bane of most engineering apprentices, however its versatility and appropriateness far outweighs the hard work it requires, or is perceived to require. Its effective use requires skill and concentration. An often overlooked advantage of scraping is the ability to take the tool to the work piece. When the work piece weighs several tons and towers over the worker, the apprentice's solution of chucking it on the mill is impractical, if not impossible. A skilled craftsman can wield a scraper and produce work that is the envy of his peers. This takes more time than the usual methods.

Putty KnifeSometimes referred to as a spackle knife, the putty knife is a scraping tool that is constructed in a manner that is similar to the kitchen spatula. Distinguished by a flat blade that is equipped with a sturdy handle, the putty knife can be used in a number of different construction and home repair projects. Putty knives are available in two distinct types, with each type being geared toward specific applications.

The stiff blade style of putty knife is constructed with a solid metal blade that is somewhat thick and does not bend easily. This type of putty knife is ideal for use in any job where there is a need for a rigid tool. One example of a task that the stiff blade putty knife is uniquely suited for is scraping. The scraper action can help to remove paint or wall paper, or as a means of ridding just about any smooth surface from a foreign element.

Dust brush

It is a tool with bristles wire or other filaments. This can be used to keep surfaces clean and free of debris. It generally consists of a handle or block to which the filaments are affixed either parallel or perpendicular, depending on the way the brush is to be gripped during use.

Shave hookIt is used for cleaning and preparing lead cable sheath and sleeves for soldering and wiping joints.
and Consists of a flat hardened steel blade riveted to a shank fitted with a plastic handle. The Blade has a sharp, beveled cutting edge which is circular in shape at one end and is brought to straight sided point at opposite end. Shave Hooks feature hardened and tempered steel blades, riveted to shanks which run through the full length of the specially shaped handle.

Chisel knifeIt is a tool for checking the adhesion of the paintings on their substrate.
A knife with a square edge, usually 1 ½ in. (3.8 cm) or less in width, used to scrape off paint or wallpaper in areas where a wider-edged stripping knife would not be suitable. Traditional tradesmans quality tool with one piece through tang tempered stainless steel blade for strength and durability, complete with hardwearing rosewood scales handle.

Nail Punch

A nail punch, also called a nail set, is used to drive the head of a nail flush with or below a surface. A pin punch is a similar tool used to drive pins for affixing a fixture to a rotating shaft. Nail and pin punches have a body by which the punch is held, with a flat ended cylindrical section whose diameter suits the object to be driven.

Wednesday, April 23, 2014

Electrical cables

Electrical cables are used to transmit electricity, and they are made up of two or more wires bonded together (through twisting or braiding). These wires are covered by protective and insulating material. There are many different types of electrical cables, and they are typically categorized depending on such factors as electrical conductivity, type of insulation, type of protector (or covering), weight, cost, and specific uses.

•A cable is an assembly of one or more conductors (wires) with some flexibility.
•A lead is a complete assembly of cable and connectors.
•A wire is a single conductor which may have an outer layer of insulation (usually plastic).

Types of cables

•Single and multi-strand conductors

Solid wire, also called solid-core or single-strand wire, consists of one piece of metal wire.

Multi-strand wire Single –strand
wire

Stranded wire or multi strand conductor is composed of a bundle wires to make a larger conductor.

Stranded wire is more flexible than solid wire of the same total cross-sectional area. Solid wire is cheaper to manufacture than stranded wire and is used where there is little need for flexibility in the wire. Solid wire also provides mechanical ruggedness; and because it has relatively less surface area which is exposed to attack by corrosives, protection against the environment.

Stranded wire is used when higher resistance to metal fatigue is required. Such situations include connections between circuit boards in multi-printed-circuit-board devices, where the rigidity of solid wire would produce too much stress as a result of movement during assembly or servicing; A.C. line cords for appliances; musical instrument cables; computer mouse cables; welding electrode cables; control cables connecting moving machine parts; mining machine cables; trailing machine cables; and numerous others.

Single-cored and multi-cored cables

Single core

Single core cable is mostly used for industrial applications where it is run in conduits. In domestic wiring it is usually only used for certain situations such as for electric fittings.

Multi Core

Colours used for the cable insulation

Electrical wires have markings stamped or printed on the outside sheath of the cable. These markings tell what type and size of wire that you have. And also the color of the wires inside of the sheath reveals that different color wires serve different purposes.

Purpose

Colour

Protective earth (PE)

Green/yellow bi-colour

Neutral (N)

Blue

Single phase: Live (L)
Three phase: L1

Brown

Three phase: L2

Black

Three phase: L3

Grey

Flexible
cables colour code

No. of cores

Colours

2 core

Brown , Blue

3 core

Brown , Blue , Green and yellow

4 core

Brown , Blue , Green and yellow ,
Black or grey

5 core

Brown , Blue , Green and yellow ,
Black or grey , Black or grey

Basic
types of electrical accessories used for domestic single phase circuits.

Mounting Box

Mounting
boxes protect connections between two or more wires or between wires and
switches or fixtures. Mounting boxes are available with different sizes
and made of different materials such as ABS, plastic , PVC and etc…

Switches

An electrical switch
controls the flow of power in an electrical circuit. It provides an open
circuit in the off position and acts as a closed circuit in the on position.

Types of
switches

·

Single
Pole Switches

This is the simplest type of switch. Most residential
switches are single pole switches.

Single pole switch with
neon indicator

Single pole switch
without neon indicator

·Double Pole Switches

These types of switches are often used to switch mains
electricity because it can isolate both the live and neutral connections at
once.

Socket outlet

Socket outlets
are used when temporary electrical connections are required. eg : for
connecting table lamp , table fan , radio ,etc……There are two types of socket
outlets available in the market.

I.Two
pin type (live, neutral)

II.Three
pin type ( live , neutral and earth)

As all
appliances connected by flexible leads should be earthed, two pin type is
outdated today. The 3 pin type is standardized for domestic wiring and use at
2,5,13 and 15 A rating.

Ceiling rose

Ceiling rose is
used to connect pendant lamps, ceiling fans and etc… to the supply system.
Ceiling rose consist of two main parts called base and cover. Both the parts
are made up of Bakelite or porcelain. Terminals are provided on the base and a
hole is made in the cover to take out the flexible wire.

Junction box

Junction boxes
are used in electrical installation to join some conductor and provide
different paths for different conductors. Most of the junction boxes are made
of plastic.

Cable clips

Cable clips are
used to attach electrical cables to a wall or baseboard. Based on the cables
that are used, suitable type of cable clips should be selected.

Sunday, April 13, 2014

Hand tools are the tools which are used by human in a workshop for various electrical installation related works and also for various maintenance works.

Types of hand tools

1.Screw driver
A hand tool used to fix and remove screws. Used in assembling work and maintenance work. Available in three main types:

a)Flat type – Point of the screw driver is flat shape used for straight slot screws.
b)Pozidriv type (Philips type) - Point of the screw driver is special shape (x shape) to match with the slot in pozidriv slot screw. Used for Pozidriv slot screws.
c)Offset screw driver – Designed for use in confined areas where it is impossible to use a standard screw driver.

2.Pliers

A hand tool, used to hold smaller components for various activities such filing, drilling etc. We can cut wires pulled out tighten small components by using pliers.

3.Hammer
A hand tool used for delivering blows (force) in chipping using chisel, bending, straightening and other operations. Hammers are forged from high carbon steel. Hammer sizes are specified by their weight. Main types of hammers are:

a)Ball pein hammer – Most commonly used hammer. Consists of flat face for general work and ball pein for peining or riveting.
b)Cross pein hammer – Used for sheet metal forming
c)Straight pein hammer – Used for sheet metal work

4.Tape measure

A tape measure is a portable measurement device used to quantify the size of an object or the distance between objects. The tape is marked along the tape edge in inches and fractional inches, typically in quarter-, eight-, and sixteenth-inch increments. Some tape measures are marked in millimeters, centimeters, and meters on one edge.
The most common tape measures are 12 feet, 25 feet, or 100 feet in length.

•Portable electric Drilling machine
Electrically operated hand drill. Used for rough and small diameter hole drilling (up to about 18mm dia.)Spindle is driven by the electric motor and feeding of drill is done by human hand. Can drill metals also.

•Hammer drill

A hammer drill has a specially designed clutch that allows it to not only spin the drill bit, but also to punch it in and out (along the axis of the bit). Hammer drills are more expensive and more bulky than regular drills, but are preferable for applications where the material to be drilled—concrete block or wood studs—is unknown. For example, an electrician would use a hammer drill for attaching items (such as an electrical box) to either wood studs (if used as a conventional power drill) or masonry walls (if used as a hammer drill).

Drill bit
The cutting tool used on a drilling machine is known as a Drill bit ( Drill). The most common type of drill is Twist Drill.
Twist drill
Twist drill is consists of 2 main parts:
i)Body – A cylindrical part make with 2 helical flutes to provide the cutting lips and cutting point to remove the chips. To reduce the friction of the body and the point against the walls of the hole and for better guiding of the tool, only a part of the cylindrical surface is left project and form what are called the lands.
ii)Shank – The part of the drill which to the machine. Depend on the method of applied to securing the drill, the shank available as
a)Straight or Cylindrical type – Available as drills which are less than 12.7mm in diameter. When fixing the straight shank drills to a drilling machine a Drill chuck or a Collet chuck is used.
b)Taper Shank – Consists of standard Morse taper shank. Available as drills which are more than 12.7mm in diameter. When fixing the taper shank drills to a drilling machine the Morse tapered spindle hole or Morse tapered sleeve is used.

Monday, April 7, 2014

Pipes are used in water supply systems to deliver water from one place to another. Water flaws through pipes by:
Gravity or
Force pumping

For efficiency, pipes must deliver water with least friction. For this reason pipes are usually circular and the inner surface is made smooth. Man has used many materials for the manufacture of pipes. In the first instance bamboo trunks were used as pipes by boring through the nodes. Then pipes were made by twisting lead sheet around circular timber. Later hot drawn, cold drawn or seam welded pipes were manufactured from metals like copper, steel, stainless steel, aluminum and brass etc. In large water supply installations pipes made out of:-
Cast iron
Black iron
Concrete
Asbestos were used.
A major disadvantage of these pipes was that they are heavy and joining was complicated. During World War 2 the necessity for a more flexible and convenient pipe type was felt and the result was the synthetic polymer pipe.

Polymer Pipes - The advantages of polymer pipes are:
a)Easily moulded to any shape or size
b)Easy to work with and are light weight
c)High resistance to weathering and corrosion
d)Almost maintenance free
e)Good electrical, sound and heat insulation
f)Withstand moisture, oils and acids.

Plastics (polymers) are mainly divided into 02 groups:-

•Thermoplastics - which become soft on heating and returning back to its original form on cooling

•Thermosetting plastics - which undergo chemical changes on heating and do not return to original form on cooling

Polymer (plastic) pipes are a petroleum bi-product. Two main plastics are used in the manufacture of pipes namely:-
–PVC (Poly Vinyl Chloride)
–HDPE (High Density Polyethylene)

PVC is identified as a rigid pipe while HDPE is identified as a flexible pipe. Polymer pipes are manufactured by extrusion or moulding.

These need special pipe components which are named pipe fittings. There are various pipe fittings used for the different requirements and locations:
Bends (90˚ or oblique), Elbows, Reducers, Tees (equal/unequal), Sockets (Plain/valve/faucet), Union couplings

Union coupling Elbow

Tee Bend

‘Y’ junction

Valves and Taps
(or faucets)

Valves and taps
(faucets) are required in pipe systems to control flow. Flow control includes -
Increase flow, Decrease flow, Stop flow or Open flow.